239. 滑动窗口最大值

class Solution 
{
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) 
    {
        vector<int> res;
        deque<int> q;
        for(int i = 0;i < nums.size();i ++)
        {
            //看滑动窗口是否大于k
            if(q.size() && i - k + 1 > q.front()) q.pop_front();
            //维持一个严格单调下降的双端队列
            while(q.size() && nums[q.back()] <= nums[i]) q.pop_back();
            q.push_back(i);//把当前下标放入双端队列中
            //滑动窗口大小满足k
            if(i >= k - 1) res.push_back(nums[q.front()]);
        }
        return res;
    }
};